• 한국수학사학회지
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• 제32권1호
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• pp.17-25
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• 2019

This essay elucidates the way the geometries of space-time theories explain material bodies' motions. A conventional attempt to interpret the way that space-time geometry explains is to consider the geometrical structure of space-time as involving a causally efficient entity that directs material bodies to follow their trajectories corresponding to the laws of motion. Newtonian substantival space is interpreted as an entity that acts but is not acted on by the motions of material bodies. And Einstein's curved space-time is interpreted as an entity that causes the motions of bodies. This essay argues against this line of thought and provides an alternative understanding of the way space-time geometry explain the laws of motion. The workings of the way that Newton's flat and Einstein's curved space-time explains the law of motion is such that space-time geometry encodes the principle of inertia which specifies straight lines of moving bodies.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.1-19
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• 2016

In this study, the supersonic panel flutter of doubly curved composite sandwich panels with variable thickness is considered under aerothermoelastic loading. Considering different radii of curvatures of the face sheets in this paper, the thickness of the core is a function of plane coordinates (x,y), which is unique. For the first time in the current model, the continuity conditions of the transverse shear stress, transverse normal stress and transverse normal stress gradient at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are satisfied. The formulation is based on an enhanced higher order sandwich panel theory and the vertical displacement component of the face sheets is assumed as a quadratic one, while a cubic pattern is used for the in-plane displacement components of the face sheets and the all displacement components of the core. The formulation is based on the von $K{\acute{a}}rm{\acute{a}}n$ nonlinear approximation, the one-dimensional Fourier equation of the heat conduction along the thickness direction, and the first-order piston theory. The equations of motion and boundary conditions are derived using the Hamilton principle and the results are validated by the latest results published in the literature.

• 한국수학사학회지
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• 제22권3호
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• pp.273-292
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• 2009

뉴턴과 아인슈타인의 시공간에 대한 표준적 해석에 의하면 독립적으로 존재하는 시공간이란 존재자가 물체의 운동을 인과적으로 설명한다. 이 논문은 뉴턴과 아인슈타인의 시공간을 해석하는 이 견해를 비판적으로 고찰한다. 이두 이론에서 시공간을 해석하는 최근 과학사와 과학철학의 연구를 중심으로 필자는 시공간 구조가 운동법칙의 부산물이지 그 반대가 아님을 주장한다. 이러한 시공간의 동역학적 견해를 통해 시공간이 가지는 인과적 속성이 뉴턴물리학에서 아인슈타인 물리학으로의 이론변화의 발전에 의미 있는 기능을 하지 못하였음을 주장할 것이다.

• 한국전자파학회논문지
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• 제30권1호
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• pp.60-69
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• 2019

본 논문에서는 전방 관측 특히, 곡선운동을 하는 차량용 전방 관측 역산란 합성 영상 형성에 대해 다룬다. 영상 형성을 위해 시간 영역 상관관계(time domain correlation: TDC) 기법이 사용되었으며, 차량의 전방 지면의 2D 영상을 얻는다. TDC는 공간변화 시스템에 대한 정합 필터링을 구현한 기법이므로 가우시안 잡음에 강건하다. 또한, 직선운동을 할 때의 영상과 곡선운동을 할 때의 영상에 대한 비교, 분석을 통해 곡선운동을 했을 때 영상의 엔트로피가 증가하는 대신 영상의 분해능이 향상되었음을 보인다.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.535-550
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• 2005

The non-linear static and dynamic response of doubly curved thin isotropic shells has been studied for the step and sinusoidal loadings. Dynamic analogues Von Karman-Donnel type shell equations are used. Clamped immovable and simply supported immovable boundary conditions are considered. The governing nonlinear partial differential equations of the shell are discretized in space and time domains using the harmonic differential quadrature (HDQ) and finite differences (FD) methods, respectively. The accuracy of the proposed HDQ-FD coupled methodology is demonstrated by the numerical examples. Numerical examples demonstrate the satisfactory accuracy, efficiency and versatility of the presented approach.

• Advances in aircraft and spacecraft science
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• 제8권4호
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.

• Steel and Composite Structures
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• 제24권2호
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• pp.151-176
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• 2017

This paper deals with general equations of motion for free vibration analysis response of thick three-layer doubly curved sandwich panels (DCSP) under simply supported boundary conditions (BCs) using higher order shear deformation theory. In this model, the face sheets are orthotropic laminated composite that follow the first order shear deformation theory (FSDT) based on Rissners-Mindlin (RM) kinematics field. The core is made of orthotropic material and its in-plane transverse displacements are modeled using the third order of the Taylor's series extension. It provides the potentiality for considering both compressible and incompressible cores. To find these equations and boundary conditions, Hamilton's principle is used. Also, the effect of trapezoidal shape factor for cross-section of curved panel element ($1{\pm}z/R$) is considered. The natural frequency parameters of DCSP are obtained using Galerkin Method. Convergence studies are performed with the appropriate formulas in general form for three-layer sandwich plate, cylindrical and spherical shells (both deep and shallow). The influences of core stiffness, ratio of core to face sheets thickness and radii of curvatures are investigated. Finally, for the first time, an optimum range for the core to face sheet stiffness ratio by considering the existence of in-plane stress which significantly affects the natural frequencies of DCSP are presented.

• 한국공간구조학회논문집
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• 제18권1호
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• pp.93-100
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• 2018

The retractable roof structures have actions of various types of loads and external forces depending on the retraction and operation conditions of the roof in terms of efficiency of control and maintenance as the aspect of structural plan. In particular, there is a need for studies on the establishment of retraction controlled wind velocity to maintain the stable control and usability of roof structure against strong winds or sudden gusts during the retraction of the roof. In this paper, it was intended to provide basic materials for the development of guidelines on the operation and maintenance of domestic retractable buildings with large space by analyzing the factors affecting the retraction controlled wind velocity for the overseas stadiums with the large spatial retractable roof structures where the sliding system was applied on the steel retractable systems. As a result, the controlled wind velocity tends to decrease as the retractable roof area increases. On the other hand, the controlled wind velocity tends to increase as the retraction time increases. In addition, in the space-grid roof structures, the spherical roof structures type showed the average controlled wind velocity of 10m/sec lower than that of 17.3m/sec for curved-roof structure type, and in the curved-roof structure type, the truss roof structure showed the average controlled wind velocity of 8.9m/sec which is lower than that of 17.3m/sec for the space for the space-grid roof structure.

• 한국실내디자인학회논문집
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• 제24권6호
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• pp.128-136
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• 2015

This research, which has been planned to appreciate the features of continuous observation of space, has applied the procedure of acquiring continuous visual information when the act of watching takes place along the time to analyze the space characteristics through the scenes and time so that the features of attention shown in the process of acquiring visual information at the time of observing continuous scenes might be estimated. For analysis of the features of continuous observation was set up the premise that the features of observation and perception vary depending on gender, when the women shops in department stores were selected as research objects. The observation features found at the time of continuous observation of selling spaces in department stores were focused on two analysis methods in order to compare the differences and characteristics of the two. The followings are the findings. First, the area with predominant observation was found to be 87.1% in both methods. It was found that the analysis of observation features by "Analysis I" was useful for inter-sectional comparison of continuous images. Second, in case of extracting predominant sections, the ceiling or the structures which are the backgrounds rarely attracted any eyes. Depending on analysis method, there was the gap of 14.3%~25.0% between observed sections. Third, in case that the hall is curved, the eyes were found to be expanded from side to side and up and down. The review of observation numbers of predominant sections makes it possible to decide whether it should be regarded as (1) unstability or (2) expanding search, and when the images are enlarged from distant view to close-range view, the weakening vanishing point results in the increase of expanded search of surroundings. Accordingly, it was found that the characteristics of images has effects on the observation features when any space was continuously observed. Furthermore, the difference of analysis methods also was found to be likely to cause big differences in the results of analyzing observation features.

• 한국실내디자인학회논문집
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• 제15권5호
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• pp.95-103
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• 2006

Ron Arad, the master of contemporary design in the U.K., is one of representative leaders of this age who has left distinguished achievements in the history of contemporary design through innovative design. Analyzing and understanding the Deconstructive design concept and the deconstructive characteristics of interior space of Ron Arad will contribute to finding directions for today's design and laying the ground for explaining the development pattern of design in the 21st century. After analyzing the deconstructive characteristics of each selected space, One Off and Ron Arad Associates have shown a deconstructive design trend of a creative formula by using methods that shed conventional processes and material while a space composition and form of new concept was attempted in the resting space of the New Tel Aviv Opera House, offering not only the establishment of a new circulation system, but also diverse experiences of space to visitors. Likewise, a temporal experience and communication between the user and the space was attempted in Belgo Noord and Belgo Central by partially applying a narrative space composition that sheds existing design concepts. At the Millennium House, they have produced an interior space for future house developed by breaking off from existing typical design development work and material through computer operation, and made various forms of space and atmosphere possible by attempting variable elements and the use of ultramodern material. Y's fashion shop has granted variability to the form and volume of space according to time by presenting display elements that have shed existing form and function. Hotel Puerta America as well, with a curved structure that has broken off with existing forms and maximized space variability through structures that have utilized ultramodern materials and instruments. Through this study, it has been verified that Ron Arad has been unraveling connections between interior space and its user, its requirements, and the original unique principles of space by applying deconstructive design concepts, and that through the mediation of these spaces, he is attempting indirect communication with the user. Eventually, he is taking part in the harmony and development of all elements of space connected with human beings by applying deconstructive design concepts.